Yeah, like
@ScottB said, Vibrant had a
lack of detectable anything that wasn't in Algaefix. No carbon sources, etc. It's not like it had the algaefix ingredients + some special stuff.
To understand the complexity of nutrients moving around with using algaefix etc, think about making a bunch of algae cells suddenly leaky. So what exactly gets released? sugars, amino acids, etc hard to say. (there's a paper on algae getting exposed to these polymers ending up releasing higher levels of dissolved free amino acids)
Depends on what organisms are in the tank, which ones are more and less affected by the algaecide, and what their condition is - how much stored goodies are in their cells?
So now that stuff gets released - bacteria gobble it up, and depending on the details of what's released - this may basically look to bacteria like a carbon dose resulting in lower measurable PO4 , NO3 etc.
Dan exposed some algae containers he grew to the algaecide and tracked PO4. in some it stayed the same, in some it went down, in others it went up a bit. The details of what it hits and how hard matters a lot, it would seem.